In Japanese Patent Application No. 62-19371 (published under No. 63-191580) the applicant has proposed a controller for operating a dust collector synchronously with another power tool such as an electric plane. In use, the controller is plugged into a wall receptacle. The controller has two receptacles. An electric plane is plugged into one receptacle, while a dust collector is plugged into the other receptacle. The electric plane and the dust collector are connected to each other by a hose. When the electric plane is switched on, the electric plane and the dust collector start at the same time. Thus, the dust collector absorbs dust produced by the electric plane, through the hose, while the electric plane is operating. When the electric plane is switched off, the dust collector also stops simultaneously.
Another prior mechanism for operating a dust collector synchronously with another power tool is simpler, and includes a receptacle provided in the dust collector for supplying another power tool. The dust collector is plugged into a wall receptacle. Another power tool is plugged into the receptacle of the dust collector. The dust collector is first switched on. However, the dust collector does not start. Then, the other power tool is switched on. Thereupon, the two apparatus start at the same time. Switching off the other power tool stops the dust collector simultaneously with the other power tool.
The latter synchronizing mechanism also includes a switch provided in the dust collector for switching the operational setting of the dust collector from independent to synchronous, or vice versa. For discussion's sake, let it be supposed that an electric plane is another power tool to be operated synchronously with the dust collector. For synchronous operation, the user sets the dust collector for synchronous operation. At the same time, before plugging the electric plane into the dust collector, he usually ensures that the power switches of the two apparatus are both OFF. By so doing, he can ensure complete safety. However, even in the event he plugs one into the other without ensuring it, he will not get into danger if at least one of the two power switches fortunately happens to be OFF. However, if he plugs one into the other when the two power switches are both ON, the two apparatus will unexpectedly start the very moment he plugs one into the other. It is a dangerous situation.
Usually the power switch of the dust collector is OFF when the user plugs the dust collector into a wall receptacle. The operational setting of the dust collector is an independent operation or a synchronous operation. However, if its setting is already a synchronous operation and at the same time its power switch is ON, plugging the dust collector into a wall receptacle does not start it. Thus, in such a case, it is possible that the user may erroneously assume that the power switch of the dust collector is OFF. He may be more careless about the power switch of the electric plane than about that of the dust collector because he will not get into danger if he plugs the electric plane into the dust collector when the power switch of the latter is ON, provided the power switch of the former is OFF. Thus, it is desirable to provide a synchronizing mechanism which enables the user to automatically ensure that the power switch of the dust collector is OFF when the power tool with which the dust collector is to be operated synchronously is not plugged into the dust collector.